N-Cbz-L-Valinal cyanohydrin (I) is converted into imidate (II) and then condensed with 2-aminophenol (III) to afford benzoxazole (IV). Removal of the N-Cbz group of (IV) with H2 and Pd/C provides amine (V), which is then coupled to N-Cbz-valyl proline (VI), yielding the dipeptide amide (VII). After hydrogenolysis of the N-Cbz protecting group of (VII), the free amine (VIII) is coupled to the acid fragment (IX) by means of EDC/pyridine to furnish (X).

Oxidation of the secondary alcohol of (X) employing the Dess-Martin periodinane reagent leads to ketone (XI). The t-butyl ester group of (XI) is finally cleaved in the presence of trifluoroacetic acid to generate the title compound.